What You Two Think (Doesn't Matter)
by pricecheckgreen
Summary: Underfell Gaster, on the other hand, made no pretenses of adoption or fatherly affection.
1. Chapter 1

Part 1

 **Boogeyman**

* * *

As the record spun on the beat-up gramophone fished out and repaired from the dump, the needle scratched on its surface and produced a tune.

It wasn't one that Sans knew.

~ _Children have you ever met the boogeyman before?~_

He hated the uncontrollable way his body shivered whenever Dr. Gaster approached him, syringe in hand. It was a natural response. He knew that, of course, but it didn't stop the shame from coursing through his body. …Not that he could usually tell when the pain started to set in. At that point there wasn't room for any emotion.

Today the needle looked different, which was only significant because he couldn't focus on much else. Longer and thinner, as the scientist laid it out on a table near where he'd strapped Sans to a chair. The bastard was humming lightly as he rifled through his medicine cabinet.

 _~No of course you haven't for you're much too good I'm sure~_

Sometimes, depending on which lab room he was in and who else was involved, it was possible to get a few glimpses of the test sheet—read bits and pieces of the words that made sense and try to puzzle out what exactly was expected of him, or whatever process was being tested on him. But today it was out of his reach. He had nothing to do but squirm and watch Gaster work, slowly being eaten alive by anticipation.

Today was a bad day. He knew it would be. He couldn't stop the shaking.

He wanted to yell, _why the fuck didn't you have everything ready before you got me out here_ , but the words were stuck in his teeth.

 _~If the boogeyman should ever come to visit you~_

Whatever he was looking for wasn't there in the first cabinet he tried, and Gaster bent down to look under his sink. Completely at ease, humming in that odd, disjointed way he did. There was a bit of a clatter as he upended some beakers and pans, drowning out the next bit of lyrics and causing Sans to almost jump out of his bones.

As Gaster pulled out a small vial of clear liquid, he began to sing quietly alongside the music.

"[ _Hush hush hush…Here comes the boogeyman.]"_

His voice didn't go along with the music—tuneless and jarring. Not that any of it was fun to listen to but hearing that _voice_ attempt to sound melodious only made it worse. It was—creepy.

It reminded him of how sweet he'd sounded when they first faced each other, Gaster with his hands behind his back and Sans with his brother's hand in a death-grip. Talking to them like they were stray animals that needed to be carefully corralled before slapping collars on their necks.

 _~Don't let him get too close to you he'll catch you if he can~_

After setting down the vial he produced from a bottom drawer a flask of something a dull blue. The flask was marked, but Sans didn't recognize any of the letters for its chemical composition. He didn't dare ask. As he watched, Gaster gently tipped the vial, pouring a few drops of the clear, water-like substance into the blue sludge.

There was a loud rushing in his ears and his vision briefly blacked out. That was normal for the restrained tests. Sometimes the fear would get to be too much. But he still chided himself and violently shook his head, trying to retain the anger. The anger was good. It was just hard to stay angry at things that happened so routinely.

~ _Say shoo shoo, and stick him with a pin~_

The two fluids mixed and flared a brilliant, deep red.

 _"_ [Marvelous.]"

It didn't look right. There looked like shapes, dark shadows whirling and floating around in the bottle. He wanted to say something. Tell him that he needed to mix a different one, it looked all wrong. But it felt like his teeth were glued together. And Gaster had started joining in with the record again. He could hear that the song was skipping, perhaps because of the damage to the record.

 _"[Say buzz buzz, just like the wasp that stings.]"_

His soft singing was even harder to listen to than the faded voice on the gramophone.

The doctor took the needle that he'd set down and carefully slipped it into the flask, drawing out the fluid. Sans began to quiver. He didn't want that inside him. He didn't want to have his bones broken off again.

"d-d-doctor g-gaster-"

A thin finger moved to lay across his mouth, silencing him. "[What have I told you about speaking out of turn, Sans?]"

Gaster didn't sound angry but could tell he was treading a thin line. "you c-can't-" It was still hard to talk. He hated it. He hated himself. "-c-concentrate when i-keep t-talking."

"[And we wouldn't want to have any…accidents while I am doing these delicate procedures, would we?]"

Sans swallowed and shook his head.

Satisfied, Gaster examined his syringe before pulling back to start up some equipment behind them-an orange light flaring up, something he didn't quite understand. "[Almost ready.]"

It didn't make him feel better.

~ _When the shadows of the evening creep across the sky_ ~

He dug his clawed fingers into the arms of the chair as he was approached once more, preparing himself for the pain, the snapping of his ulna. But it didn't come.

~ _And your mommy comes upstairs to sing a lullaby_ ~

The pinpricks of Sans' pupils were swallowed by darkness as Gaster went to hold the side of his face, steadying the syringe in his hand.

"[We are going to try something different today, Sans.]"

He steadied the syringe and suddenly with a sick twist inside his ribs Sans understood.

As the record skipped again, the needle pointed.

Right.

At.

His.

Eye.

"[ _Hush hush hush…Here comes the boogeyman.]"_

He brought the needle into Sans' eyesocket like an ice pick.

* * *

 **Author's Note** : I don't intend for this to be nearly as extensive as the Undertale Gaster fic, however I do plan to post 3 chapters on the relationship between Underfell Gaster, Sans, and Papyrus that was hinted at in my Evil Laughing fic.


	2. Chapter 2

Part 2

 **Bonus**

* * *

-Sometimes being in the labs felt as natural as breathing. Looking at his reflection in the linoleum floor, his nasal aperture burning on the smell of chemicals. It felt like he'd always been there, it felt like it was where he belonged. Those times he would respond to questions and prodding with an unusual acuity, nudge pieces of machinery into place should he see something out of sorts. …Perhaps hoping for praise. Some of the other scientists would slip him a candy bar or a band-aid if he helped them with their calculations.

Then, sometimes, like today, it choked him. Sometimes he felt he was drowning in darkness. Sometimes he ached for freedom so intensely that he wanted to destroy himself and hope that the dust he left behind got carried outside in a draft.

But then, it wasn't like there was any fresh air and sky outside the lab waiting for him there.

 _SANS, TELL ME WHAT IT'S LIKE OUTSIDE._

Pain curled into his eyesocket, lighting his pupil like a flame.

 _don't you remember?_

He screamed and screamed until eventually Gaster found the noise to be annoying and covered his mouth to muffle the sound.

 _ONLY A LITTLE._

The injection finished, Sans was unstrapped from the chair allowed to collapse to the floor, pressing down on his eye as though to try smothering the pain.

 _it's still a hellhole._

He burned on the inside and whimpered as he was picked up by the back of his shirt and dragged.

 _it's still a prison._

The hallway floor tiles scraped on his leg bones as he was taken back to his cell and thrown in, startling the other skeleton sitting inside.

 _just a bit bigger than this one, that's all._

Gaster tsked and scrawled down some notes on his clipboard. "[We are going to have to have a follow-up exam when you have recovered a little more. I doubt you'll be of much use to me in this state.]"

 _SANS?_

Sans struggled to get to his feet as the bars were put back in place, keeping them trapped inside.

 _IS THERE A GASTER OUT THERE, ON THE OUTSIDE?_

When the dark shadow of the scientist receded down the hallway only then did he turn his flaring eye back at his brother.

 _of course there is._

"WHAT DID HE DO?" Papyrus reached out a trembling hand as though to touch the luminescent red pupil quivering in Sans' socket. "WHAT DID HE DO?"

 _BUT DON'T YOU THINK IT WOULD BE EASIER TO RUN?_

"don't touch it." He pressed back against the wall. "it hurts, don't touch it."

 _WITHOUT BARS IN THE WAY?_

His brother ignored the plea, pulling Sans' hand away and touching the outer rim of the socket.

 _there's no point in running._

By that point of course the howling was reduced to a hoarse whimper, and then, suddenly, a flush of anger.

 _everywhere is more of the same._

His eye was a bright, glimmering red.

* * *

Papyrus was much quieter in his checkups with the doctor than he was in conversation with his brother. Speaking when spoken to, lowering his voice was much as he was able. Perhaps he was intimidated or perhaps he simply had better manners—there was no way to be sure. But whatever the reason, the two of them maintained at least a relative calm with each other that was a nice…palate cleanser, of sorts.

It was only occasionally that he would punctuate the scribbles of Gaster's pencil on paper with questions.

"DO YOU ENJOY HURTING HIM?"

He was in the middle of recording Papyrus' rate of growth, which had slowly started to overtake that of his brother's. To feign disinterest in the question he continued writing for a few more seconds before finally looking up and saying, "[What?]"

Papyrus shrank from the doctor's gaze, looking down at his feet dangling off the table. "THAT'S WHAT SANS SAID. …THAT YOU ENJOY HURTING HIM. …THAT THAT'S WHY YOU KEEP US HERE."

There appeared to be some fear in his tone, despite the volume-that there would be retribution for asking something so boldly. Though Papyrus had never been hurt in the labs. Never been tortured. Just measured. Poked and prodded and asked questions.

Gaster sighed and put down his clipboard. "[When did he tell you that, hm? Just recently?]"

"IT WAS AFTER…AFTER HE CAME BACK WITH HIS NECK CHIPPED. …AND HE SAID THAT."

"[I see.]" The scientist leaned back against the counter, slotting his pinkie into his teeth and chewing. He didn't seem upset. Just thoughtful. The same expression that came over his face when he noted things like growth rates and power development. Rather than pain tolerance.

Papyrus didn't mind giving the doctor something to think about. It delayed the hammer test, if he was going to get it today.

He did not enjoy the hammer test.

"[Sans is approaching things from a biased perspective, Papyrus. Understand that, first. He is the one who typically suffers in the name of science. Naturally, he starts to think that his suffering is the goal.]" Gaster shrugged. "[This is not so.]"

"BUT YOU DO HURT HIM. I HEAR HIM SCREAMING. WHY DO YOU HURT HIM IF YOU'RE NOT TRYING TO?"

Despite the conflict etched into Papyrus' creased brow the older skeleton merely returned to writing notes, pausing to give the occasional glance for confirmation of whatever features he was making record of. "[I do hurt him. The reasons why, I think are…a little complicated to explain to someone of your mental caliber.]"

"IS IT IMPORTANT? DO YOU HAVE TO?" The boy began to bite his finger as well-the sharpness of his teeth almost doing damage.

Gaster didn't respond for a moment, merely reaching over to pull Papyrus's hand out of his mouth. "[What I am doing is not for pure torment's sake. It is…experiments. Testing ideas using him. New methods of defending monsters. New plans for breaking the barrier that keeps us all trapped.]" He looked thoughtful, curved eye closing.

"…AND YOU HAVE TO?"

"[The experiments are necessary for the kingdom. …For Asgore. I could not stop performing them even if I wanted to. The pain I inflict while carrying them out is…well…]"

A smirk twisted his mouth.

"[…A pleasant bonus.]"

It was true that Sans was in the unfortunate position of being one of the only subjects he could use with impunity. Asgore would not stand for the randomized abduction of his citizens. No matter how vital Gaster would argue that it was. It would cause too much unrest, he said. Too much rebellion. He was already on thin ice.

But no one cared about a couple of orphaned street rats.

Papyrus was growing.

At the outset he had only worked on the one. Ostensibly because Sans had promised his cooperation if he spared his brother, not knowing what had been in store for him. But really because Papyrus was too young and fragile to get any meaningful work done.

But he was getting bigger. His magical ability was much more pronounced. His bones less thin.

"[Would you spare him his suffering?]"

The question was sudden, and it made Papyrus look up in surprise, jaw opened slightly. "WOULD I…? -YES OF COURSE."

Dr. Gaster's brow twitched, his broken eye narrowing and the smirk widening. "[Would you?]"

" _YES_ , I JUST SAID THAT!"

"[Would you spare him if it meant sacrificing yourself?]"

Papyrus opened his mouth. No words came out. His fingers dug in deeper where they clutched the edge of the table and he looked down once more.

He felt sudden breath on his face and his entire body froze.

"[You would fare much, much better than he, I think.]" Gaster's voice was soft, and crooning, almost. Like a parent speaking to a baby. "You are stronger. You might be a little smaller yet but you will grow to be bigger than him. And you know how to _behave_."

Much of his best work was something he had to hold off on for fear of breaking his only useable subject. He would dearly love to have a bonus waiting on the sidelines.

Gaster's cold fingers curled into Papyrus' jaw. "[So I'll ask you again, dear boy. Would you spare him his-]"

"-n-NO."

The suddenness of the response did seem to startle the scientist away, head tilting a little. He opened his mouth to speak and at first nothing came out. Then the grin returned. "[No? Well then there's no need to discuss that right now, is there? …I think I am finished with your evaluation.]"

The little skeleton gripped the table harder, his whole body coursing with shame. He didn't want to go back to the cell. He didn't want to see Sans in his fitful sleep. See that eye flaring and sparking in his socket as he dreamed.

"[I'm sure he's very proud to have you as a brother.]"

Papyrus said nothing, hopping down from the table and allowing himself to be led back to his room, his hand in one so much bigger than his.

When they came back, Sans was sleeping, curled almost up into a ball. There was a faint red glow from under his lids. Excess magic burning him up inside. Unlike last night though, he wasn't shivering and clearing his throat continuously. So there was progress.

He hadn't wanted to wake his brother but the bars rattled when Gaster opened the cell door, and Sans sprang up with a harsh, frightened gasp. Probably because he thought it meant he was next. For the first time he felt not annoyance or bewilderment but pure shame.

The scientist merely chuckled and nudged Papyrus inside. When he had them both secure he walked away, whistling. Leaving the yet smaller of the two to wring his hands and look down at his unadorned feet.

"I'M SORRY."

Sans only stared before crawling off to his corner again.

* * *

 **Author's Note:** My life is picking up a bit-I'm moving to a new place and starting classes back up again, for one thing. So my productivity rate is likely going to slow down somewhat. But, I had this chapter mostly written so I thought I might as well finish it up and have at least one more thing posted.


End file.
